Castalia is a city in Winneshiek County, Iowa, United States. The population was 145 at the 2020 census. The railroad was built throug…Castalia is a city in Winneshiek County, Iowa, United States. The population was 145 at the 2020 census. The railroad was built through Castalia in 1864. Castalia was incorporated in 1902. According to the United States Census Bureau, the city has a total area of 0.58 square miles, all land.